Among the following chemical reactions the irreversible reaction is

Options

A. `PCl_(5)(g) to PCl_(3)(g)+Cl_(2)(g)`
B. `Pb(NO_(3))_(2)(l) +2KI(l) to PbI(2)(s)+2KNO_(3)(l)`
C. `CaCO_(3)(s) to CaO(s) +CO_(2)(g)`
D. `2SO_(2)(g)+O_(2)(g) to 2SO_(3)(g)`

Answer

To determine which of the given chemical reactions is irreversible, we need to analyze the nature of each reaction based on the information provided.

### Step-by-Step Solution:

1. **Understanding Reaction Types**:
- Irreversible reactions are those that proceed in one direction and do not readily revert to the reactants. Common examples include combustion, neutralization, and certain precipitation reactions.
- Reversible reactions can proceed in both directions, meaning the products can convert back to reactants under certain conditions.

2. **Analyzing the Given Reactions**:
- The question indicates that we need to evaluate several reactions, but we will focus on the characteristics of the types mentioned.
- **Gaseous Reactions**: If a reaction involves gases and occurs in a closed container, it is often reversible. This is due to the ability of gases to expand and contract, allowing for both forward and reverse reactions.
- **Neutralization Reactions**: These typically involve an acid and a base reacting to form water and a salt. Neutralization reactions are generally irreversible because the products (water and salt) do not revert back to the original reactants under normal conditions.
- **Precipitation Reactions (PPD)**: These reactions often lead to the formation of a solid from soluble reactants, and they are usually irreversible as the solid precipitate does not dissolve back into the solution easily.

3. **Identifying the Irreversible Reaction**:
- From the analysis, we can conclude that the neutralization reaction is a strong candidate for being irreversible.
- If we consider the example given in the transcript (e.g., Pb(NO3)2 + KI → PbI2 + KNO3), this is a precipitation reaction and is also irreversible.

4. **Conclusion**:
- Among the reactions mentioned, the one that is clearly irreversible is the neutralization reaction or the precipitation reaction, such as the formation of PbI2 from Pb(NO3)2 and KI.

### Final Answer:
The irreversible reaction among the given options is the neutralization reaction or the precipitation reaction (e.g., Pb(NO3)2 + KI → PbI2 + KNO3).

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